a) Field of the Invention PA1 b) Description of the Related Art
The present invention relates to a printed circuit, and more particularly to a printed circuit structure using a flexible printed circuit.
A flexible printed circuit (FPC) is made of a flexible film of resin such as polyimide on which a circuit pattern of copper foil or the like is formed, and is characterized in its flexibility. In this specification, a "flexible printed circuit (FPC)" is intended to include a tape carrier package. Also, the term "flexible printed circuit" should include both a relatively thin sheet-shaped printed circuit and a relatively thick board-shaped printed circuit. The flexible printed circuit may also be called a "flexible printed circuit cable (FPCC)".
In electronic apparatuses having movable units, such as printers, a flexible printed circuit is used as a wiring member for electrically connecting a movable unit and a fixed unit. Even in electronic apparatuses not having movable units, such as liquid crystal displays (LCD) and cameras, a flexible printed circuit is used in order to mount a wiring member in a narrow space. Flexible printed circuits are used in both applications on the assumption that they are bent.
A flexible printed circuit is electrically and mechanically connected to an object unit (hereinafter called a main board) by solder, anisotropic conductive film (ACF) or the like. The main board is a hard board made of glass as in LCD, epoxy, glass epoxy or the like, and is hardly deformed. As a flexible printed circuit is bent or subjected to vibrations or temperature change, a stress is generated which is concentratedly applied to a connection portion between the flexible printed circuit and main board. If the connection strength at the connection portion is insufficient, the flexible printed circuit is peeled off in some cases, from the main board by the applied stress. In order to increase the connection strength, after a flexible printed circuit is connected to a main board, UV curing agent or other curing agents have been coated on the surfaces of the main board and flexible printed circuit. Even with such countermeasure, the connection strength is still not sufficient in some cases. Moreover, this countermeasure increases the number of manufacture processes and raises production cost.
As described above, a flexible printed circuit once connected to a main board may be peeled off by applied stress.